The present invention relates to a single seal and, more specifically, to a seal for a rotary shaft extending through a wall, e.g. a pump housing wall. The single seal has one single sealing surface between a fixed and a rotary sealing ring. The sealing rings are biased towards each other by means of an axially displaceable sleeve extending through the wall. The biasing force is provided by a spring device arranged outside the pump housing.
In this context it is previously known to use springs for holding sealing packages together. For example, one such arrangement is described in U.S. Pat. No. 2,158,832. One problem with this arrangement is that the springs are arranged inside the pump housing, i.e. in the pumped medium. On the on hand, the spring arrangement is bulky, and therefore cannot be arranged within a limited space. On the other hand, when pumping liquid media, especially fluid foodstuffs, there is also a problem in that the pumped medium blocks the movement of the spring. The spring arrangement also has several pockets where the pumped medium may collect, causing hygienic problems.
Another known arrangement for sealing of a shaft extending through a wall is shown in U.S. Pat. No. 2,682,422. Compression springs are arranged outside the wall for increasing the pressure on the sealing surfaces. The spring force from the springs is transferred via two sliding rings, of which one ring rotates together with a sleeve extending through the wall. The sleeve transfers the force to the actual sealing rings. Underneath the sleeve there are further seals in the form of box plaits (packing rings) with a grease-packed spring located between them. The arrangement is a complicated construction where compressing the springs must compensate the wearing of the sliding rings. The box plaits also cause the sealing arrangement to have a high edge width.
The present invention resolves the above problems by providing a new design of single seal. Two sealing rings, one fixed and one rotating together with the shaft, are located inside the pump housing for sealing against the shaft and towards the exterior. The inner sealing ring is fastened to a sleeve extending through the pump house wall and is loaded by a tension spring device in order to increase the contact pressure against the outer sealing ring. Thanks to this design, the seal will have a very small edge width inside the pump housing. It also substantially lacks pockets where the medium may collect. The entire spring package is arranged on the atmospheric side so as to avoid the problems in connection with the pumped medium being in contact with the springs. Due to the tension springs, no further slide bearings are necessary to transfer the spring forces to the sleeve and on to the sealing rings.
The present invention thus provides a single seal for the sealing of a rotating shaft extending through a wall. The seal is mounted on the wall by means of a flange in order to seal off a chamber inside the wall against the shaft and towards the exterior. The single seal exhibits an outer and an inner sealing ring. These sealing rings are in sliding and sealing contact with each other. The outer sealing ring is fastened to the flange and the inner sealing ring is fastened to an axially displaceable sleeve. The sleeve is in turn affixed to and rotating with the shaft, and extends through the wall and the flange. The seal also has a spring device arranged outside the wall and providing a force for increasing the contact between the sealing rings.
According to the invention, the spring device comprises an inner fastening ring affixed to the sleeve and an outer fastening ring affixed to the shaft, whereby tension springs and driving pins are provided between the inner and the outer fastening rings.
The invention is defined in the appended claim 1, whereas advantageous embodiments are defined in the dependent claims.